iOS 11.4 (build 15F5037c) is an official Apple over-the-air update for the iPhone 6s, released on 2018-04-02T17:06:56Z. The update package is 262.64 MB. This is a delta (partial) update that requires 11.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 329b5b29d77c5370c63a210b83e24965e5085364.zip.